The immune system functions to protect individuals from infectious agents, e.g., bacteria, multi-cellular organisms, and viruses, as well as from cancers. This system includes several types of lymphoid and myeloid cells such as monocytes, macrophages, dendritic cells (DCs), eosinophils, T cells, B cells, and neutrophils. These lymphoid and myeloid cells often produce signaling proteins known as cytokines. The immune response includes inflammation, i.e., the accumulation of immune cells systemically or in a particular location of the body. In response to an infective agent or foreign substance, immune cells secrete cytokines which, in turn, modulate immune cell proliferation, development, differentiation, or migration Immune responses can produce pathological consequences, e.g., when it involves excessive inflammation, as in the autoimmune disorders (see, e.g., Abbas et al. (eds.) (2000) Cellular and Molecular Immunology, W.B. Saunders Co., Philadelphia, Pa.; Oppenheim and Feldmann (eds.) (2001) Cytokine Reference, Academic Press, San Diego, Calif.; von Andrian and Mackay (2000) New Engl. J. Med. 343:1020-1034; Davidson and Diamond (2001) New Engl. J. Med. 345:340-350).
Positive and negative co-stimulatory signals play critical roles in the modulation of B and T cell activity, and the molecules that mediate these signals have proven to be effective targets for immunomodulatory agents. Positive co-stimulation, in addition to T cell receptor (TCR) engagement, is required for optimal activation of naive T cells, whereas negative co-stimulation is believed to be required for the acquisition of immunologic tolerance to self, as well as the termination of effector T cell functions. Upon interaction with B7.1 or B7.2 on the surface of antigen-presenting cells (APC), CD28, the prototypic T cell costimulatory molecule, emits signals that promote T cell proliferation and differentiation in response to TCR engagement, while the CD28 homologue cytotoxic T lymphocyte antigen-4 (CTLA-4) mediates inhibition of T cell proliferation and effector functions (Chambers et al, Ann. Rev. Immunol., 19:565-594, 2001; Egen et al., Nature Immunol, 3:611-618, 2002). Several new molecules with homology to the B7 family have been discovered (Abbas et al, Nat. Med., 5:1345-6, 1999; Coyle et al., Nat. Immunol., 2: 203-9, 2001; Carreno et al., Annu. Rev. Immunol., 20: 29-53, 2002; Liang et al., Curr. Opin. Immunol., 14: 384-90, 2002), and their role in T cell activation is just beginning to be elucidated.
These new costimulatory ligands include B7h, PD-L1, PD-L2, and B7-H3. B7h (Swallow et al, Immunity, 11: 423-32, 1999), also known as B7RP-1 (Yoshinaga et al, Nature, 402: 827-32, 1999), GL50 (Ling, et al, J. Immunol., 164:1653-7, 2000), B7H2 (Wang et al, Blood, 96: 2808-13, 2000), and LICOS (Brodie et al, Curr. Biol., 10: 333-6, 2000), binds to an inducible costimulator (ICOS) on activated T cells, and costimulates T cell proliferation and production of cytokines such as interleukin 4 (IL-4) and IL-10.
PD-L1 (Freeman et al, J. Exp. Med., 192: 1027-34, 2000), also known as B7-H1 (Dong et al, Nat. Med., 5, 1365-9, 1999), and PD-L2 (Latchman et al, Nat. Immunol., 2:261-8, 2001), also known as B7-DC (Tseng et al, J. Exp. Med., 193, 839-46, 2001) bind to programmed death 1 (PD-I) receptor on T and B cells.
Finally, B7-H3 binds an as yet currently unknown counter-receptor on activated T cells, and is reported to enhance proliferation of CD4+ T helper (Th) cells and CD8+ cytotoxic T lymphocytes (CTLs or Tcs) and selectively enhance IFN-γ expression (Chapoval et al, Nat. Immunol, 2, 269-74, 2001; Sun et al, J. Immunol., 168, 6294-7, 2002).
The identification of additional molecules that have T cell costimulatory activity is of keen interest due to their fundamental biological importance and the therapeutic potential of agents capable of affecting their activity. Agents capable of modulating costimulatory signals, and thereby capable of modulating the activation and/or effector functions of CD8+ CTLs and CD4+ Th cells find use in the modulation of immune responses, and are highly desirable.
In particular, many autoimmune disorders are known to involve autoreactive T cells and autoantibodies. Agents that are capable of inhibiting or eliminating autoreactive lymphocytes without compromising the immune system's ability to defend against pathogens are highly desirable.
Conversely, many cancer immunotherapies, such as adoptive immunotherapy, expand tumor-specific T cell populations and direct them to attack and kill tumor cells (Dudley et al., Science 298:850-854, 2002; Pardoll, Nature Biotech., 20: 1207-1208, 2002; Egen et al., Nature Immunol., 3:611-618, 2002). Agents capable of augmenting tumor attack are also highly desirable.
In addition, immune responses directed against different antigens (e.g., microbial antigens or tumor antigens), while detectable, are frequently of insufficient magnitude to afford protection against a disease process mediated by agents (e.g., infectious microorganisms or tumor cells) expressing those antigens. It is often desirable to administer to the subject, in conjunction with the antigen, an adjuvant that serves to enhance the immune response to the antigen in the subject.
It is also desirable to inhibit normal immune responses to antigen under certain circumstances. For example, the suppression of normal immune responses in a patient receiving a transplant is desirable, and agents that exhibit such immunosuppressive activity are highly desirable.
Costimulatory signals, particularly positive costimulatory signals, also play a role in the modulation of B cell activity. For example, B cell activation and the survival of germinal center B cells require T cell-derived signals in addition to stimulation by antigen.
CD40 ligand present on the surface of helper T cells interacts with CD40 on the surface of B cells, and mediates many such T-cell dependent effects in B cells.
The protein BTLA (B and T lymphocyte attenuator) is a member of the CD28 family of receptors that also includes CD28, CTLA-4, ICOS, and PD-1. The initial members of the family, CD28 and ICOS, were discovered by functional effects on augmenting T cell proliferation following the addition of monoclonal antibodies (Hutloff et al. (1999) Nature 397:263-266; Hansen et al. (1980) Immunogenics 10:247-260). BTLA was discovered through screening for differential expression in TH1 cells. In addition, BTLA has been described as providing negative inhibitory signals, analogous to CTLA-4. In the presence of agonist anti-BTLA Mab, anti-CD3 and anti-CD28 activated T-cells show reduced IL-2 production and proliferation (Kreig et al., J. Immunol., 175, 6420-6472, 2005). Mice lacking an intact BTLA gene show higher titers to DNP-KLH post-immunization and an increased sensitivity to EAE (Watanabe et al., Nat. Immunol, 4, 670-679, 2003). HVEM (herpes virus entry mediator) has been shown to be a ligand for BTLA (Scully et al. (2005) Nat. Immunol. 6:90-98; Gonzalez et al. (2005) Proc. Nat. Acad. Sci. U.S.A. 102: 1116-1121).
Accordingly, agents that recognize BTLA, in particular antibodies and binding agents thereof that recognize BTLA, and methods of using such agents, are desired.
Antibodies can be used as therapeutic agents. Certain antibodies when used as a therapeutic agent in vivo can cause undesired immunogenicity of the antibodies. As most monoclonal antibodies are derived from rodents, repeated use in humans results in the generation of an immune response against the therapeutic antibody, e.g., human against mouse antibodies or HAMA. Such an immune response results in a loss of therapeutic efficacy at a minimum and a potential fatal anaphylactic response at a maximum. One approach for reducing the immunogenicity of rodent antibodies involves the production of chimeric antibodies, in which mouse variable regions (Fv) were fused with human constant regions (Liu et al. (1987) Proc. Natl. Acad. Sci. USA 84:3439-43). However, mice injected with hybrids of human variable regions and mouse constant regions develop a strong anti-antibody response directed against the human variable region, suggesting that the retention of the entire rodent Fv region in such chimeric antibodies may still result in unwanted immunogenicity in patients.
Additionally, grafting of rodent complementarity determining region (CDR) loops of variable domains onto human frameworks (i.e., humanization) has been used to further minimize rodent sequences. Jones et al. (1986) Nature 321:522; Verhoeyen et al. (1988) Science 239:1534. However, CDR loop exchanges still do not uniformly result in an antibody with the same binding properties as the antibody of origin. Changes in framework residues (FR), residues involved in CDR loop support, in humanized antibodies also are often required to preserve antigen binding affinity. Kabat et al. (1991) J. Immunol. 147:1709. While the use of CDR grafting and framework residue preservation in a number of humanized antibody constructs has been reported, it is difficult to predict if a particular sequence will result in the antibody with the desired binding, and sometimes biological, properties. See, e.g., Queen et al. (1989) Proc. Natl. Acad. Sci. USA 86:10029, Gorman et al. (1991) Proc. Natl. Acad. Sci. USA 88:4181, and Hodgson (1991) Biotechnology (NY) 9:421-5. Moreover, most prior studies used different human sequences for animal light and heavy variable sequences, rendering the predictive nature of such studies questionable. Sequences of known antibodies have been used or, more typically, those of antibodies having known X-ray crystal structures, such as antibodies NEW and KOL. See, e.g., Jones et al., supra; Verhoeyen et al., supra; and Gorman et al., supra. Exact sequence information has been reported for a few humanized constructs.
The need exists for anti-BTLA antibodies, and in particular anti-BTLA monoclonal antibodies, for use in treatment of human disorders, such as inflammatory, autoimmune, and proliferative disorders. Such antibodies will preferably exhibit low immunogenicity in human subjects, allowing for repeated administration without adverse immune responses.